Control device for hot blast stoves



March 9, 1937.

D. M, EVANS CONTROL DEVICE FOR HOT BLAST STOVES Filed Sept. 12, 1934 2a INVENTOR 0R06 /V. {VA/v5.

' ATTORNEY Patented Mar. 9. 1937 UNITED STATES PATENT OFFICE CONTROL DEVICE FOR HOT BLAST STOVES Drue M. Evans, Wood River, lll., assignor to Petroleum Conversion Corporation, New York, N. Y., a corporation of Delaware Application September 12, 1934, Serial No. 743,745

4 Claims.

My present invention relates to improvements in devices for operating hot blast stoves, or other types of regenerative heaters designed to furnish heated gas or air at a constant temperature. Bat- 5 teries of such stoves have been used for many years in the steel industry for the heating of air. In recent years use has been made of hot blast stoves to heat a combustible gas of hydrocarbon nature to serve as a heat carrying medium for the cracking of oils, reference being had to the patent to Knox No. 1,715,239, dated May 28, 1929. A hot blast stove consists of a suitably enclosed mass of heat absorbing material, usually checker bricks, provided with means for heating the same l5 by combustion of fuel, and also with means for passing a 4stream of the gas or air to be heated over such checker bricks after the same have been heated up and the ring stopped. It is obvious that the temperature of the gas or air so heated 20 will begin to drop as the mass of checker bricks cools down, so that unless means are provided i'or adjusting the temperature of the gas or air its temperature will be non-uniform. It is, therefore, customary to mix the gas as it leaves the 25 heated stove with a varying amount of cold gas so as to keep the mixture at a relatively constant or uniform temperature, such gas, as a rule, being by-passed from the so-called coldblast main supplying the cold gas to the stove to the so-called 30 hot blast main conducting the heated gas awayV from the stove. It has also been proposed to employ an automatic means in the by-pass for sup-` plying a regulated quantity of the tempering gas.`

point, it is not possible to obtain a satisfactoryv automatic control of the temperature at the exit end of the hot blast main (at which point the regulation is desired) because of the lag of tern-v perature in the main itself.

It is accordingly an object of my present inven tion to provide an automatic means for regulating the amount of gas by-passed adjacent-'theV exit end of the hot blast main while-admitting the bulk supply of the temperinggas at the inlet end.

By virtue of this arrangement, moreover, a -much4 smaller valve may be used for the temperature 55 controlthan whenI it is attempted to use-a single (Cl. 19E- 132) valve, thereby rendering the control valve more sensitive. y

In carrying outmy invention I therefore provide a main tempering valve adjacent the inlet end of the hot blast main, and a thermostatically con- 5 trolled auxiliary valve adjacent the exit end of said main. It is apparent-that during the heat yielding or blast period, the main by-pass valve must be throttled at intervals in order to provide a working rangefor the auxiliary valve. This l0 may either be accomplished by hand or by means controlled by the auxiliary valve or byY other means. Preferably, and as shown, the position of the main valve is automatically controlled by the y operation of the auxiliary valve.

A further feature of my invention consists in the provision of a mixing chamber for the gas and the oil substance to be cracked, which preferably is in vapor form, arranged between the hot blast main and the reaction chamber (in which latter, 20 time is afforded forcarrying out the cracking reaction) and the location of the temperature responsive device in the connection between the mixing chamber rand the reaction chamber. YBy virtue of this arrangement, the automatic control. of the tempering gas may compensate not only for variations in the temperature'of the gas as it leaves the stovey but also for any variation inthe temperature of theoil vapor to be cracked.

My invention will be best understood by reference to the following detailed description taken with the annexed drawing, invwhich Figure 1 shows the layout of a battery of hot blast stoves forming part of a system for cracking hydrocarbon oils to which my invention has been applied; Figure 2 is anenlarged diagrammatic View; partly in section, showing the details of my irnproved arrangement forjproviding simultaneous control of the main and auxiliary valves; and

Figure 3 is an enlarged view taken on line 3-,3 of Figure 2.

In Figure 1, I0 denotes the individual members` of the battery of three hot blast stoves shown, while II denotes the cold blast main feedingthe relatively cold gas to the stoves through connections not shown; I3 denotes the hot blast main having individual connecting pipes I4, I5kand I6, respectively, to the three stoves. The main bypass at the inlet end of the main I3 is denoted I8, 50 While the auxiliary by-pass at the exit'end of the main is indicated by 20. Avalve I9, hereinafter to be described', is provided in saidV main I8. In the system illustrated the hot gas is fed from the exitend `01:' the main I3 into mixing chamber 22, 55

in which the gas is mingled with the hydrocarbon vapor to be cracked, which is fed to said chamber through pipe 24 from a source not shown. The mixture of hot gas and vapor passes from the mixing chamber through pipe 25 to interiorly insulated chamber 26 which is the reaction chamber and in which the reaction of cracking takes place.

In the system illustrated, it is desirable that the mixture leaving the mixing chamber be at a uniform temperature inasmuch as variation of this temperature will effect to an undesirable degree a disturbance in the equilibrium of the oil cracking system, and accordingly the temperature responsive element 36 is, under these circumstances, placed in said pipe 25, although it is obvious that the system of temperature regulation will apply in precisely the same way if said element be placed in the exit end of the hot blast main i 3 at a point past the union therewith of the auxiliary by-pass 26.

n The temperature responsive element 30 is part of a temperature control device 3|, Which may be of standard construction, and inasmuch as per se it forms no part of the present invention, it has not been illustrated in detail. The device 3| merely operates to maintain-a given temperature in the pipe 25, which may be varied as called for by controlling the operation of a motor 33. In apparatus for accomplishing this, Which is a standard article of manufacture, when the temperature falls below the point which is set, a mercury tipping cell is actuated to drive a motor 33 in a direction which will close the valve in by-pass 26, whereas when the temperature rises above the point set, the mercury cell is tipped to actuate another circuit which will operate the motor 33 in the reverse direction to open said valve. Referring to the valve now denoted 35 in the by-pass 26, this may consist of a gate or slide 36 having an opening therein 37, which when the valve is fully open will register with the internal bore 38 constituting a portion of the by-pass 26. The slide 36 is guided by means of a yoke 40 in conjunction with fins 4|, integral with the slide. The slide 36 is moved back and forth by means of threaded shaft 43 in engagement therewith. This shaft in turn is driven by means of a shaft 45 through worm 44' thereon which engages a worm wheel on the shaft 4 3, shown in Figure 2. Shaft 45 is driven by motor 33 preferably through gear reduction box 45a and a friction clutch 46 so as to prevent injury to the parts if for any reason the motor should not be stopped when the slide 36 has reached its limit of travel.

Accordingly, in the system as thus far described, variations in temperature in the pipe 25 will be corrected by the automatic operation of the valve 35 acting to by-pass a variable quantity of cold gas from main Since, however, the amount of cold gas by-passed is a minor part of that by-passed through pipe |8, means are preferably provided for automatically throttling valve I3 in said pipe when valve 35 approaches its limit of travel. As one means for accomplishing this, the following mechanism is provided.

Valve I9 in the main by-pass I8 may be assumed to be the same type as valve 35, and its movement is controlled by motor 50 which operates same through gear train 5|, 52 and the threaded shaft 53. Ordinarily, both valves will be water cooled, means for accomplishing this not being shown for the sake of simplicity. When slide 36 of valve 35 approaches its closing limit a shoe 55, which is threaded to shaft 45 (and insulated therefrom) and consequently moves up and down in response to the rotation of said shaft, is moved downwardly to close a circuit through a pair of contacts 56, 5l, a circuit then being established through conductors 56a and 51a to actuate a solenoid 66, Figure 3. Solenoid 60 has an armature 6| pivotally joined through a link 6|b to a pawl arm 6 la which has a pawl 62 and is loosely mounted on a shaft 64. Pawl 62 engages ratchet 62a rotatably iixed to shaft 64. Also mounted on shaft 64 is a commutator 63 having an interrupted annular conductor 65. The action of the solenoid is thus to cause the commutator to be moved by the pawl which will cause the conductor 65 to close the circuit through contacts 66 and 61, which normally are in contact with the interrupted or non-conducting portion of said conductor 65. The circuit established through contacts 66, 61 includes the starter 6B for motor 50, which thereupon sets the motor 56 in operation to move the slide 53 in a closing direction. When motor 50 rotates it also drives shaft 64 through gear reduction box 69 and friction clutch 10, which latter permits movement of commutator 63 by pawl 62 independently of motor 50, the friction in said clutch being maintained by spring Ha. Shaft 64 is, therefore, rotated until the circuit through contacts 66, 61 is broken by the conductor 65 of commutator 63 leaving said contacts. This interruption of the circuit stops motor 50, which has now accomplished closing of valve I9 by a suitable increment. The partial closing of said valve serves to increase the temperature of gas in the main I3 slightly, which rise in temperature causes the temperature responsive element to set into operation the valve 35, the arrangement loe-V ing such as to preferably cause said valve to open to almost its maximum degree of travel. If for any reason the valve I9 should not close in time, thereby causing the temperature in the main 23 to rise to such a point that it cannot be handled by the valve 35, then shoe 55 will establish a circuit through contacts 12, 13 to sound an alarm T5, which circuit also operates to stop the motor 50 by suitable actuation of the starter 68. The operation of motor 5|), moreover, is susceptible of manual control by means of the nut 1|, by which the commutator 63 may be moved independently of the action of motor 56.v

It will thus be seen that accurate control of the gas temperature is had while permitting the bulk of the tempering gas to be added at the inlet end of the hot blast main. By the use of the relatively small auxiliary valve 35, the control can be made more sensitive than if it attempted to control one large valve. Thus, the volume of gas by-passed at the start of the heating cycle is so large (equal, say, to 50% by volume of the hot gas) that exact regulation of the temperature by the main by-pass valve alone would be diiiicult even if the tempering gas were added at the exit end of the hot blast main where the lag in temperature therein would not be a factor. Ordinarily, the auxiliary by-pass valve would not be more than one-third the capacity of the main by-pass valve. As previously indicated, when my invention is applied to a system of cracking oils, advantage is taken of this sensitiveness of control to also compensate for any variation in temperature of the oil vapor admitted through pipe 24 as by the location of the temperature responsive element 30 in the pipe 25 whereby the temperature of the mixture of vapor to be cracked and the heated gaseous carrier may be controlled and kept uniform with great accuracy.

It will be understood that the invention is applicable to other sources of hot gas than socalled hot blast stoves, especially Where such source of gas is subject to considerable variation in temperature.

I claim:

l. In an oil cracking system wherein oil is cracked by mixing the vapor of the oil with a heated gaseous heat carrier, a battery of hot blast stoves, a hot blast main common to the members of said battery, a source of relatively cold gas which may be admixed with the heated gaseous heat carrier to control the temperature of same, a main by-pass from said source to said hot blast main adjacent the inlet end thereof, a regulating valve in said by-pass, an auxiliary by-pass from said source to said main adjacent the outlet end of said main, a mixing chamber for said heated gas and the oil in vapor form to be cracked to which said hot blast main is joined, means for introducing oil vapor to be cracked into said mixing chamber, a reaction chamber, a connection from said mixingA chamber to said reaction chamber, means responsive to the temperature of the materials mixed in said mixing chamber prior to their substantial introduction into said reaction chamber, and a valve in said auxiliary by-pass for regulating the amount of gas admitted through said auxiliary by-pass said valve being controlled by said temperature responsive means.

2. In an oil cracking system wherein oil is cracked by mixing the vapor of the oil with a heated gaseous heat carrier, a battery of hot blast stoves, a hot blast main common to the members of said battery, a source of relatively cold gas which may be admixed with the heated gaseous heat carrier to control the temperature of same, a main by-pass from said source to said hot blast main adjacent the inlet end thereof, a regulating valve in said by-pass, an auxiliary bypass from said source to said main adjacent the outlet end of said main, a mixing chamber for said heated gas and the oil in vapor form to be cracked to which said hot blast main is joined, means for introducing oil vapor to be cracked into said mixing chamber, a reaction chamber, a connection from said mixing chamber to said reaction chamber, a temperature responsive element in said connection to control the temperature of said heat carrier gas supplied to said mixing chamber by automatically regulating the amount oi.' cold gas admitted through said auxiliary bypass.

3. In an oil cracking system wherein oil is cracked by mixing the vapor of the oil with a heated gaseous heat carrier, a source of hot gas, a hot gas main conveying the heated gas from said source, a source of relatively cold gas which may be admixed with the heated gaseous heat carrier to control the temperature of same, a main by-pass from said source to said hot gas main adjacent the inlet end thereof, a regulating valve in said by-'pass, an auxiliary by-pass from said source to said main adjacent the outlet end of said main, a mixing chamber for said heated gas and the oil in vapor form to be cracked to which said hot gas main is joined, means for introducing oil vapor to be cracked into said mixing chamber, a reaction chamber, a connection from said mixing chamber to said reaction chamber, means responsive to the temperature of the materials mixed in said mixing chamber prior to their substantial introduction into said reaction chamber, and a valve in said auxiliary by-pass for regulating the amount of gas admitted through said auxiliary by-pass, said valve being controlled by said temperature responsive means.

4. In an oil cracking system wherein oil is cracked by mixing the vapor of the oil with a heated gaseous heat carrier, a source of hot gas, a hot gas main conveying the heated gas from said source, a source of relatively cold gas which may be admixed with the heated gaseous heatcarrier to control the temperature of same, a main bypass from said source to said hot gas main adjacent the inlet end thereof, a regulating valve in said by-pass, an auxiliary by-pass from said source to said main adjacent the outlet end of said main, a mixing chamber for said heated gas and the oil in vapor form to be cracked to which said hot gas main is joined, means for introducing oil vapor to be cracked into said mixing chamber, a reaction chamber, a connection from said mixing chamber to said reaction chamber, means responsive to the temperature of the materials mixed in said mixing chamber prior to their introduction into said reaction chamber, and a valve in said auxiliary by-pass for regulating the amount of gas admitted through said auxiliary by-pass, said valve last mentioned being controlled by said temperature responsive means, means for automatically closing said main valve in response to the action of said auxiliary valve by increments permitting a Working range to be had by said auxiliary valve.

DRUE M. EVANS. 

